Energy storage systems have become increasingly used to deliver power to utility grids either as part of standalone energy storage systems or as part of a renewable energy source (e.g. wind generation or solar generation systems) with an integrated energy storage system. Energy storage systems (e.g., battery banks or integrated cells of other energy storage devices) can be particularly helpful when used for frequency stabilization applications in grid connected renewable energy sources. Renewable energy sources can require frequency stabilization features to address the variability that exists within the renewable energy source and help deliver constant active and reactive power to the utility grid. In some grid-tied frequency regulation or frequency response applications, an energy storage system can be charged when the grid frequency is too high and discharged when the grid frequency is too low.
The batteries or other energy storage devices used in grid frequency regulation applications are designed to account for various performance criteria, including size, energy capacity, life expectancy and the like. For example, batteries can be sized at installation to have more energy capacity at the beginning of life (BOL) than is needed, so that as battery capacity degrades over time they will still have enough capacity at end of life (EOL). In some applications, batteries are sized to have 20-50% more capacity at BOL than they do at EOL.
Higher battery performance capabilities at BOL can result in system inefficiencies due to overperformance and excess device wear without compensation. Since batteries have a larger energy capacity window in which to operate at BOL, the batteries will cycle through more Mega-watt-hours (MWh) per day at BOL than at end of life (EOL). The system will effectively behave like gas in a container and use all the available space. This will result in a higher performance score at BOL, but the battery system may not be paid for that higher score and thus gives away performance without being compensated. The increased MWh that cycle through the battery degrade the battery at a faster rate than is necessary.